What does backslash dot mean as a command?

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A software I installed inserted a line in my profile that reads:

[ -s "$SOME_FILE" ] && . "$SOME_FILE"

I know dot . is synonymous with source, so I suspect this is just sourcing the file, but I have never seen . before; does it do something else?

Edit, regarding DVs: searching for "backslash dot" leads to questions regarding ./ when calling executable files, and man source leads to a manpage where . does not appear. I don't know what else to try, hence the question.

Edit 2: see related questions

• Why start a shell command with a backslash


• Backslash at the beginning of a command


• Why do backslashes prevent alias expansion


• Run a command that is shadowed by an alias

bash

share|improve this question

edited 22 hours ago

psmears

43328

asked yesterday

Sheljohn

5113519

add a comment | 

up vote
11
down vote

favorite

2

A software I installed inserted a line in my profile that reads:

[ -s "$SOME_FILE" ] && . "$SOME_FILE"

I know dot . is synonymous with source, so I suspect this is just sourcing the file, but I have never seen . before; does it do something else?

Edit, regarding DVs: searching for "backslash dot" leads to questions regarding ./ when calling executable files, and man source leads to a manpage where . does not appear. I don't know what else to try, hence the question.

Edit 2: see related questions

• Why start a shell command with a backslash


• Backslash at the beginning of a command


• Why do backslashes prevent alias expansion


• Run a command that is shadowed by an alias

bash

share|improve this question

edited 22 hours ago

psmears

43328

asked yesterday

Sheljohn

5113519

add a comment | 

up vote
11
down vote

favorite

2

up vote
11
down vote

favorite

2

2

A software I installed inserted a line in my profile that reads:

[ -s "$SOME_FILE" ] && . "$SOME_FILE"

I know dot . is synonymous with source, so I suspect this is just sourcing the file, but I have never seen . before; does it do something else?

Edit, regarding DVs: searching for "backslash dot" leads to questions regarding ./ when calling executable files, and man source leads to a manpage where . does not appear. I don't know what else to try, hence the question.

Edit 2: see related questions

• Why start a shell command with a backslash


• Backslash at the beginning of a command


• Why do backslashes prevent alias expansion


• Run a command that is shadowed by an alias

bash

share|improve this question

edited 22 hours ago

psmears

43328

asked yesterday

Sheljohn

5113519

A software I installed inserted a line in my profile that reads:

[ -s "$SOME_FILE" ] && . "$SOME_FILE"

I know dot . is synonymous with source, so I suspect this is just sourcing the file, but I have never seen . before; does it do something else?

Edit, regarding DVs: searching for "backslash dot" leads to questions regarding ./ when calling executable files, and man source leads to a manpage where . does not appear. I don't know what else to try, hence the question.

Edit 2: see related questions

• Why start a shell command with a backslash


• Backslash at the beginning of a command


• Why do backslashes prevent alias expansion


• Run a command that is shadowed by an alias

bash

share|improve this question

edited 22 hours ago

psmears

43328

asked yesterday

Sheljohn

5113519

share|improve this question

share|improve this question

edited 22 hours ago

psmears

43328

edited 22 hours ago

psmears

43328

edited 22 hours ago

psmears

43328

43328

asked yesterday

Sheljohn

5113519

asked yesterday

Sheljohn

5113519

asked yesterday

Sheljohn

5113519

5113519

add a comment | 

add a comment | 

2 Answers
2

active

oldest

votes

up vote
23
down vote



accepted

A backslash outside of quotes means “interpret the next character literally during parsing”. Since . is an ordinary character for the parser, . is parsed in the same way as ., and invokes the builtin . (of which source is a synonym in bash).

There is one case where it could make a difference in this context. If a user has defined an alias called . earlier in .profile, and .profile is being read in a shell that expands aliases (which bash only does by default when it's invoked interactively), then . would trigger the alias, but . would still trigger the builtin, because the shell doesn't try alias expansion on words that were quoted in any way.

I suspect that . was changed to . because a user complained after they'd made an alias for ..

Note that . would invoke a function called .. Presumably users who write functions are more knowledgeable than users who write aliases and would know that redefining a standard command in .profile is a bad idea if you're going to include code from third parties. But if you wanted to bypass both aliases and functions, you could write command .. The author of this snippet didn't do this either because they cared about antique shells that didn't have the command builtin, or more likely because they weren't aware of it.

By the way, defining any alias in .profile is a bad idea because .profile is a session initialization script, not a shell initialization script. Aliases for bash belong in .bashrc.

share|improve this answer

edited yesterday

answered yesterday

Gilles

501k1169851510

add a comment | 

up vote
7
down vote

The . is a "literal dot", i.e. just a dot. It will be taken as the standard . command (similar to source in bash).

The POSIX standard has this to say about this (my emphasis)

A <backslash> that is not quoted shall preserve the literal value of the following character, with the exception of a <newline>. If a <newline> follows the <backslash>, the shell shall interpret this as line continuation. The <backslash> and <newline> shall be removed before splitting the input into tokens. Since the escaped <newline> is removed entirely from the input and is not replaced by any white space, it cannot serve as a token separator.

The dot character can be aliased:

$ alias .='echo hello'
$ .
hello

which means that . would avoid using the aliased version of the . command, because,

After a token has been delimited, but before applying the grammatical rules in Shell Grammar, a resulting word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda

100k13199310

• 
  
  
  

  
  

  
  
  
  
  
  

  
  I was looking for official source about how backslash in a word is interpreted as quoting, and how this prevents alias expansion. Thanks for the reference!
  – Sheljohn
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @Sheljohn See updated answer.
  – Kusalananda
  yesterday
  

  
  
  
  

add a comment | 

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

active

oldest

votes

active

oldest

votes

up vote
23
down vote



accepted

A backslash outside of quotes means “interpret the next character literally during parsing”. Since . is an ordinary character for the parser, . is parsed in the same way as ., and invokes the builtin . (of which source is a synonym in bash).

There is one case where it could make a difference in this context. If a user has defined an alias called . earlier in .profile, and .profile is being read in a shell that expands aliases (which bash only does by default when it's invoked interactively), then . would trigger the alias, but . would still trigger the builtin, because the shell doesn't try alias expansion on words that were quoted in any way.

I suspect that . was changed to . because a user complained after they'd made an alias for ..

Note that . would invoke a function called .. Presumably users who write functions are more knowledgeable than users who write aliases and would know that redefining a standard command in .profile is a bad idea if you're going to include code from third parties. But if you wanted to bypass both aliases and functions, you could write command .. The author of this snippet didn't do this either because they cared about antique shells that didn't have the command builtin, or more likely because they weren't aware of it.

By the way, defining any alias in .profile is a bad idea because .profile is a session initialization script, not a shell initialization script. Aliases for bash belong in .bashrc.

share|improve this answer

edited yesterday

answered yesterday

Gilles

501k1169851510

add a comment | 

up vote
23
down vote



accepted

A backslash outside of quotes means “interpret the next character literally during parsing”. Since . is an ordinary character for the parser, . is parsed in the same way as ., and invokes the builtin . (of which source is a synonym in bash).

There is one case where it could make a difference in this context. If a user has defined an alias called . earlier in .profile, and .profile is being read in a shell that expands aliases (which bash only does by default when it's invoked interactively), then . would trigger the alias, but . would still trigger the builtin, because the shell doesn't try alias expansion on words that were quoted in any way.

I suspect that . was changed to . because a user complained after they'd made an alias for ..

Note that . would invoke a function called .. Presumably users who write functions are more knowledgeable than users who write aliases and would know that redefining a standard command in .profile is a bad idea if you're going to include code from third parties. But if you wanted to bypass both aliases and functions, you could write command .. The author of this snippet didn't do this either because they cared about antique shells that didn't have the command builtin, or more likely because they weren't aware of it.

By the way, defining any alias in .profile is a bad idea because .profile is a session initialization script, not a shell initialization script. Aliases for bash belong in .bashrc.

share|improve this answer

edited yesterday

answered yesterday

Gilles

501k1169851510

add a comment | 

up vote
23
down vote



accepted

up vote
23
down vote



accepted

A backslash outside of quotes means “interpret the next character literally during parsing”. Since . is an ordinary character for the parser, . is parsed in the same way as ., and invokes the builtin . (of which source is a synonym in bash).

There is one case where it could make a difference in this context. If a user has defined an alias called . earlier in .profile, and .profile is being read in a shell that expands aliases (which bash only does by default when it's invoked interactively), then . would trigger the alias, but . would still trigger the builtin, because the shell doesn't try alias expansion on words that were quoted in any way.

I suspect that . was changed to . because a user complained after they'd made an alias for ..

Note that . would invoke a function called .. Presumably users who write functions are more knowledgeable than users who write aliases and would know that redefining a standard command in .profile is a bad idea if you're going to include code from third parties. But if you wanted to bypass both aliases and functions, you could write command .. The author of this snippet didn't do this either because they cared about antique shells that didn't have the command builtin, or more likely because they weren't aware of it.

By the way, defining any alias in .profile is a bad idea because .profile is a session initialization script, not a shell initialization script. Aliases for bash belong in .bashrc.

share|improve this answer

edited yesterday

answered yesterday

Gilles

501k1169851510

A backslash outside of quotes means “interpret the next character literally during parsing”. Since . is an ordinary character for the parser, . is parsed in the same way as ., and invokes the builtin . (of which source is a synonym in bash).

There is one case where it could make a difference in this context. If a user has defined an alias called . earlier in .profile, and .profile is being read in a shell that expands aliases (which bash only does by default when it's invoked interactively), then . would trigger the alias, but . would still trigger the builtin, because the shell doesn't try alias expansion on words that were quoted in any way.

I suspect that . was changed to . because a user complained after they'd made an alias for ..

Note that . would invoke a function called .. Presumably users who write functions are more knowledgeable than users who write aliases and would know that redefining a standard command in .profile is a bad idea if you're going to include code from third parties. But if you wanted to bypass both aliases and functions, you could write command .. The author of this snippet didn't do this either because they cared about antique shells that didn't have the command builtin, or more likely because they weren't aware of it.

By the way, defining any alias in .profile is a bad idea because .profile is a session initialization script, not a shell initialization script. Aliases for bash belong in .bashrc.

share|improve this answer

edited yesterday

answered yesterday

Gilles

501k1169851510

share|improve this answer

share|improve this answer

edited yesterday

edited yesterday

edited yesterday

answered yesterday

Gilles

501k1169851510

answered yesterday

Gilles

501k1169851510

answered yesterday

Gilles

501k1169851510

501k1169851510

add a comment | 

add a comment | 

up vote
7
down vote

The . is a "literal dot", i.e. just a dot. It will be taken as the standard . command (similar to source in bash).

The POSIX standard has this to say about this (my emphasis)

A <backslash> that is not quoted shall preserve the literal value of the following character, with the exception of a <newline>. If a <newline> follows the <backslash>, the shell shall interpret this as line continuation. The <backslash> and <newline> shall be removed before splitting the input into tokens. Since the escaped <newline> is removed entirely from the input and is not replaced by any white space, it cannot serve as a token separator.

The dot character can be aliased:

$ alias .='echo hello'
$ .
hello

which means that . would avoid using the aliased version of the . command, because,

After a token has been delimited, but before applying the grammatical rules in Shell Grammar, a resulting word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda

100k13199310

• 
  
  
  

  
  

  
  
  
  
  
  

  
  I was looking for official source about how backslash in a word is interpreted as quoting, and how this prevents alias expansion. Thanks for the reference!
  – Sheljohn
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @Sheljohn See updated answer.
  – Kusalananda
  yesterday
  

  
  
  
  

add a comment | 

up vote
7
down vote

The . is a "literal dot", i.e. just a dot. It will be taken as the standard . command (similar to source in bash).

The POSIX standard has this to say about this (my emphasis)

A <backslash> that is not quoted shall preserve the literal value of the following character, with the exception of a <newline>. If a <newline> follows the <backslash>, the shell shall interpret this as line continuation. The <backslash> and <newline> shall be removed before splitting the input into tokens. Since the escaped <newline> is removed entirely from the input and is not replaced by any white space, it cannot serve as a token separator.

The dot character can be aliased:

$ alias .='echo hello'
$ .
hello

which means that . would avoid using the aliased version of the . command, because,

After a token has been delimited, but before applying the grammatical rules in Shell Grammar, a resulting word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda

100k13199310

• 
  
  
  

  
  

  
  
  
  
  
  

  
  I was looking for official source about how backslash in a word is interpreted as quoting, and how this prevents alias expansion. Thanks for the reference!
  – Sheljohn
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @Sheljohn See updated answer.
  – Kusalananda
  yesterday
  

  
  
  
  

add a comment | 

up vote
7
down vote

up vote
7
down vote

The . is a "literal dot", i.e. just a dot. It will be taken as the standard . command (similar to source in bash).

The POSIX standard has this to say about this (my emphasis)

A <backslash> that is not quoted shall preserve the literal value of the following character, with the exception of a <newline>. If a <newline> follows the <backslash>, the shell shall interpret this as line continuation. The <backslash> and <newline> shall be removed before splitting the input into tokens. Since the escaped <newline> is removed entirely from the input and is not replaced by any white space, it cannot serve as a token separator.

The dot character can be aliased:

$ alias .='echo hello'
$ .
hello

which means that . would avoid using the aliased version of the . command, because,

After a token has been delimited, but before applying the grammatical rules in Shell Grammar, a resulting word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda

100k13199310

The . is a "literal dot", i.e. just a dot. It will be taken as the standard . command (similar to source in bash).

The POSIX standard has this to say about this (my emphasis)

A <backslash> that is not quoted shall preserve the literal value of the following character, with the exception of a <newline>. If a <newline> follows the <backslash>, the shell shall interpret this as line continuation. The <backslash> and <newline> shall be removed before splitting the input into tokens. Since the escaped <newline> is removed entirely from the input and is not replaced by any white space, it cannot serve as a token separator.

The dot character can be aliased:

$ alias .='echo hello'
$ .
hello

which means that . would avoid using the aliased version of the . command, because,

After a token has been delimited, but before applying the grammatical rules in Shell Grammar, a resulting word that is identified to be the command name word of a simple command shall be examined to determine whether it is an unquoted, valid alias name.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda

100k13199310

share|improve this answer

share|improve this answer

edited yesterday

edited yesterday

edited yesterday

answered yesterday

Kusalananda

100k13199310

answered yesterday

Kusalananda

100k13199310

answered yesterday

Kusalananda

100k13199310

100k13199310

• 
  
  
  

  
  

  
  
  
  
  
  

  
  I was looking for official source about how backslash in a word is interpreted as quoting, and how this prevents alias expansion. Thanks for the reference!
  – Sheljohn
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @Sheljohn See updated answer.
  – Kusalananda
  yesterday
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  I was looking for official source about how backslash in a word is interpreted as quoting, and how this prevents alias expansion. Thanks for the reference!
  – Sheljohn
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @Sheljohn See updated answer.
  – Kusalananda
  yesterday
  

  
  
  
  

I was looking for official source about how backslash in a word is interpreted as quoting, and how this prevents alias expansion. Thanks for the reference!
– Sheljohn
yesterday

I was looking for official source about how backslash in a word is interpreted as quoting, and how this prevents alias expansion. Thanks for the reference!
– Sheljohn
yesterday

1

1

@Sheljohn See updated answer.
– Kusalananda
yesterday

@Sheljohn See updated answer.
– Kusalananda
yesterday

add a comment | 

 

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